As is known, stacks are currently used to discharge into the atmosphere the aggressive fumes for example of thermal power stations, of waste incineration plants, of chemical plants in general, of centralized heating stations and the like.
Each stack normally has, inside it, one or more flues which are made of metallic material, for example steel, which is covered with appropriate chemically resistant materials to ensure adequate resistance to the chemically aggressive fumes which are expelled from the flue.
Currently, steel flues are defined by a plurality of tube elements which are modular and are assembled and which are manufactured in a factory which, due to logistic reasons, is usually distant from the site of the stack.
The steel tubes are then transported from the factory to the base of the stack to be inserted therein.
Subsequently, inside or outside the stack, they are turned through 90 degrees in order to be associated, one on top of the other, by flanging, welding, spigot joints etc., so as to form the flue.
The above mentioned method for manufacturing a steel flue has several problems.
For example, steel is a material which, as is known, is easily corrodible, especially in environments with humid fumes which contain sulfuric acid, such as for example the flues of stacks.
Steel is furthermore very heavy and thus difficult to handle inside a small space such as a stack, where, as mentioned, each tube must be rotated through 90 degrees.
In addition, the transport of the various tubes which will compose the flue from the factory to the stack, apart from causing additional costs, may cause damage to the inner linings of the tubes due to the impacts which unavoidably occur during their transport, loading and unloading.
Finally, the fact should also be stressed that the coupling between the various tubes is performed by specialized personnel that must work at different heights from the ground, inside the tube to be joined, with a high level of danger as to personal injury.
In order to at least partially obviate the above problems, and most of all in order to ensure considerable resistance to chemical corrosion of the flue by the fumes and also contain the weight of said flue, instead of using metallic materials, such as steel, flues are manufactured by connecting a plurality of tube elements made of fiber-reinforced plastic or FRP.
Like steel tubes, FRP tubes are also manufactured in factories which are distant from the stack and furthermore, since they are much more delicate than steel tubes, they are more severely affected by impacts caused during their transfer from the factory to the inside of the stack.
After the FRP tubes have been carried to the base of the stack, they must sometimes be inserted horizontally inside said stack, like steel tubes, and are then rotated inside it through 90 degrees in order to be arranged vertically and be joined one above the other.
In the case of FRP tubes, there is also, with respect to steel tubes, a severe problem due to the chemical-physical characteristics of this material.
The coupling of the various FRP tubes in order to produce the flue requires the personnel to work, as with steel tubes, directly inside the flue and at different heights from the ground.
Considering that FRP is a highly flammable material, the coupling of one tube to another to form the flue entails great danger due to possible fires and/or to the possible production of toxic gases which may be generated during this operation.
If one furthermore adds to this the fact that a flue has a considerable draught, it is understood that the danger for the personnel working at its manufacture is even greater than with steel tubes.